1. Field of the Invention
The invention relates in general to converter apparatus, and more specifically to power converter apparatus for interchanging electrical energy between alternating and direct current circuits.
2. Description of the Prior Art
Converter apparatus of the type which utilizes controlled rectifier devices, such as thyristors, connected to interchange electrical energy between alternating and direct current circuits, require some type of phase controller for controlling the conduction angle of the controlled rectifier devices. The conduction angle is controlled to regulate a predetermined parameter of the power converter, such as load current or load voltage.
It is important for proper operation of the converter apparatus that synchronous operation be maintained between the phase controller and power converter. In other words, the conduction angle of the gate drive signals applied to the controlled rectifier devices of the power converter must be constrained within predetermined limits, which will be referred to as rectification and inversion end stops.
U.S. Pat. No. 3,713,011 which is assigned to the same assignee as the present application, discloses an arrangement in which a single composite end stop signal is generated which is used to control all channels of the converter apparatus. The composite end stop signal is formed of segments of a plurality of timing waveforms, with the segments selected being determined by the conduction angle. The end stop signal is applied to first and second threshold circuits, which detect when the conduction angle reaches their respective limits and the conduction angle is maintained at the respective limit as long as the error signal is requesting operation beyond the limit.
While the converter apparatus and its end stop function of the hereinbefore mentioned U.S. Patent performs satisfactorily without excessive filtering, it would be desirable to reduce the cost of the converter apparatus while maintaining or improving its precision and noise immunity. It would further be desirable to be able to provide an adjustment range for one or both of the end stops, if such adjustment may be achieved without unduly increasing cost and/or circuit complexity.